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March 2007
Volume 10 / Number 3

Meeting the Challenges
of WiFi Telephony

By Ben Guderian, Feature Articles


WiFi telephony has been around since 1999, but now there’s more interest (and hype) than ever before. The frenzy around using WiFi for mobile enterprise telephony is being fueled by the promise of more dual-mode WiFi-enabled devices hitting the market. Along with that come great expectations for how these devices will drive enterprise users to hop on the corporate WiFi network and take advantage of the cost savings and additional functionality provided through integration with business IP telephony systems. Infonetics Research recently forecasted a compound annual growth rate of nearly 200 percent between 2006 and 2010 for dual-mode handsets. At the surface it may seem like all the pieces are finally coming together for enterprise WiFi telephony to go mainstream. But there are still significant challenges to meet enterprise users’ requirements for voice quality and functionality, plus the enterprise IT managers’ requirements for reliability, scalability, interoperability and security.


The Challenges

When deploying WiFi telephony in the enterprise, all of the requirements listed above need to be adequately addressed. Nonetheless, the challenges for enterprise deployment should not be viewed as roadblocks, but merely as speed bumps in the road to widespread adoption.

The challenges for enterprise WiFi telephony exist on both the network and terminal ends of the application. Enterprise WiFi network technology has come a long way in the last few years, but there are still unique issues and considerations for supporting enterprisegrade voice applications that can’t be ignored. Enterprise-grade WiFi telephone devices have also been available for some time with adoption primarily in vertical markets such as healthcare, retail stores and manufacturing plants. But with the recent proliferation of WiFi-enabled devices — primarily highend dual-mode cellular phones and PDAs — many of the concerns over WiFi telephony have resurfaced.


WiFi Network Challenges

Voice over IP (VoIP) applications present certain challenges even on wired networks, but today’s IP telephony solutions have pretty well addressed those. A well-designed IP network can support voice applications with security, voice quality, capacity and reliability that are for practical purposes every bit as good as circuit-switched PBXs. But running voice applications on WiFi networks adds a whole other dimension with unique issues and solutions. Wireless networks don’t offer the same bandwidth as wired networks, and the mobility aspect of wireless devices create some additional complications.

Bandwidth isn’t an issue in wired IP telephony. Enterprise networks have standardized on switched Ethernet with at least 10 Mbps of dedicated bandwidth for each terminal device — plenty of bandwidth for a single IP telephone set. But WiFi connections are shared by however many wireless terminals happen to be in range of an access point (AP). WiFi APs can operate at data rates as low as 1 Mbps, although most enterprise deployments are designed to operate between 11 and 54 Mbps. That’s more than sufficient for a single VoIP session, but remember, an AP may have dozens of devices including WiFi telephones and laptop computers that are simultaneously sharing bandwidth, making it critical to have some kind of quality of service (QoS) mechanism to provide preferential treatment to real-time applications like voice. A simple prioritization scheme like the WiFi Alliance’s Wireless Multimedia (WMM) specification is a good first step toward giving voice a fighting chance on a shared WiFi network. But for enterprise WiFi telephony, it takes more than just prioritization. So WMM extensions are in the works to improve bandwidth utilization (WMM Power Save) and AP capacity (WMM Admission Control). The ultimate QoS solution for enterprise WiFi telephony is some kind of scheduling mechanism to tightly control access to the wireless medium. Proprietary QoS solutions, such as SpectraLink Voice Priority (SVP), have been available to address these needs and allowed the WiFi telephony market to grow while standards continue to be developed.

The most obvious difference between wired IP telephony and WiFi telephony is the roaming aspect. Roaming isn’t an issue for most home networks, but enterprise WiFi telephone users need to be able to maintain a telephone call as they move throughout the workplace. Wired IP telephones don’t move, at least not in the middle of a telephone call, but WiFi telephones can move at any time.

WiFi protocols allow data streams to be handed off from one AP to another as the mobile device moves in and out of range of each AP. These handoffs can cause a noticeable interruption to the data stream depending on how quickly the device and AP initiate the handoff and complete whatever negotiations are necessary to start sending data again. This is where wireless security mechanisms can wreak havoc on real-time, isochronous applications like IP telephony. Fortunately, there are workable solutions available today to maintain good voice quality without compromising security, and additional standards are in the works to specifically address this issue.

There’s no real question today whether WiFi networks can support voice applications. But a voice-optimized wireless network requires the right enterprise-grade equipment and implementation following well-established best practices for WiFi telephony. WiFi network infrastructure vendors continue to innovate and bring products to market that are specifically designed with telephony applications in mind, so today’s enterprise WiFi deployments are more than likely to be designed and deployed as voice-ready.


WiFi Device Challenges

Having a voice-ready network is only half the battle. The other half deals with WiFi mobile devices and their unique challenges with supporting WiFi telephony. Just as with the network side, mobile devices have to deal with roaming issues. But there are also unique implications of WiFi telephony on device design that affect battery life — thereby also affecting device size and weight — as well as voice quality and functionality.

Starting with roaming, there is a wide discrepancy in how WiFi devices are designed to deal with mobility. At one end of the spectrum are data-specific devices like laptop computers. Laptop users aren’t expected to be highly mobile, at least not while in the middle of using a real-time application. Laptop computers can be totally reactive in handing off to another AP by waiting until the WiFi signal degrades enough to be unusable and only then searching for another AP.

At the other extreme are purpose-built WiFi telephones, which proactively search for alternative APs even while the existing signal level is at acceptable levels. Proactive roaming minimizes interruption in the data stream and allows for AP handoffs that aren’t even perceptible to the user. Unfortunately, not all WiFi devices offer proactive roaming, including many that are primarily voice devices. WiFi-enabled cellular telephones and PDAs are typically designed with the expectation that the WiFi radio will only be used for broadband data applications — primarily for Internet access over home or hotspot WiFi networks. Following the laptop computer paradigm, AP roaming is usually only reactive and unacceptable for enterprise WiFi telephony applications.

The next big device challenge for WiFi telephony is battery life. Cellular telephones have gone through many generations of improvements in radio efficiency to deliver at least several hours of talk time, and in many cases, ten hours or more. But WiFi radio technology is less mature and hasn’t been optimized to the same degree as cellular. So many WiFienabled devices suffer from significantly reduced battery life when the WiFi radio is turned on. WiFi QoS solutions improve battery life by giving the device more control over when the WiFi radio is turned on and off. But again, purpose-build WiFi telephones take advantage of these powersaving mechanisms, while most dualmode cellular phones and PDAs do not. It’s likely that, over time, we’ll see more support for power-saving schemes in dualmode cellular phones and other WiFienabled devices, particularly as support for standards like WMM Power Save become ubiquitous in WiFi radio chipsets.

There are other device challenges that aren’t necessarily technical issues, but tied to the actual device design and usage expectations. Since WiFi in a dualmode cellular phone is usually targeted at web-surfing applications, many devices have poor integration (if any) between the WiFi radio and voice resources like codecs, microphones and speakers. Some dual-mode handsets have the telephony buttons — the off-hook and on-hook keys — tied directly to the cellphone application which requires a WiFi softphone application to deal with a less-intuitive user interface. And many softphone applications that are designed for non-mobile laptop computer use aren’t capable of running on a mobile device operating system or with the limited processor power and memory of a handheld dual-mode device.


Challenges or Opportunities?

This may appear to paint a bleak picture for the real future of enterprise WiFi telephony based on where we are today. But the reality is that enterprisegrade WiFi telephony has been around and worked well for years in a variety of mission-critical applications.

Fortunately, the developers of WiFi networks and chipsets, along with handset developers, are well-aware of these shortcomings and are working on solutions to deal with them and make WiFi telephony as viable as wired IP telephony is today. There’s no question that dual-mode devices will be a significant catalyst to drive growth in enterprise WiFi telephony. But in the meantime, single-mode WiFi telephony has delivered enterprises the benefits of increased employee mobility, responsiveness and productivity while meeting their requirements within the workplace. And as standards evolve, voice will become just another application on a WiFi network, just as it has with wired networks.

Ben Guderian is the VP of Marketing at SpectraLink (news - alert) (which in the process of being acquired by Polycom (news - alert). For more information, visit the company online at http://www.spectralink. com and



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